Optical fiber coupling

Abstract

To permit operation of the light guide under widely varying temperature conditions, for example varying between -50° C. to +70° C., plug elements (5,7), for example of synthetic rubies or sapphires and retained within a hard metal sleeve (4) are formed, essentially throughout their entire cross-sectional area, with facing matching engagement surfaces. The exit or coupling plug element (5) is formed with a polished surface (15) at the side remote from the entrance plug element (7), the polished surface extending at right angles to the axis of a central duct or channel (9) which retains an optical fiber light guide. The exit or coupling plug element (5) is so positioned in the holding sleeve (4) that the polished surface (15) is located at a projecting portion beyond the terminal end (16) of the sleeve, to define a projecting distance (17). Two couplings are connected together by a housing (20). Even under contraction of the plug elements, which due to their higher temperature, coefficient than of the hard metal sleeve contract more, the facing end surfaces will remain in engagement so that no separation will occur due to a possible premature engagement of the holding sleeves of aligned couplings.

We claim: 
     
       1. Optical fiber coupling having a holding sleeve (4,4');   an entrance plug element (7) located within the sleeve;   an exit or coupling plug element (5) located within the sleeve, said plug elements including synthetic material comprising aluminum oxide, and being formed with an axial channel or duct (9) located at a central axis (8) of the respective elements within said sleeve (4,4'); and   an optical fiber element (2,2') located in said channel or duct,   and wherein, in accordance with the invention   said plug elements (5,7) are formed with facing end surfaces which are in engagement with each other essentially throughout the entire area, and retained in said sleeve (4) with said entire area engagement;   said exit or coupling plug element (5) being formed with a polished surface (15) at the side remote from the entrance plug element, which polished surface extends at right angles to the axis (8) of the channel or duct (9); and   wherein the exit or coupling plug element (5) is positioned in said holding sleeve such that an end portion of the exit plug element formed with said polished surface projects beyond a plane defining the terminal or facing end (16) of said holding sleeve (4) by a predetermined projecting distance (17).   
     
     
       2. The coupling of claim 1, wherein the channel or duct (9) in the exit or coupling plug element (5) at least in the region of said projecting distance (17) has a uniform cross-section, matched to the cross-section of the optical fiber element (2) therein. 
     
     
       3. The coupling of claim 1, wherein said predetermined projecting distance (17) of the polished surface (15) beyond the terminal end of the sleeve (16) is between about 0.005 mm and 0.5 mm. 
     
     
       4. The coupling of claim 3, wherein said projecting distance is between about 0.01 mm and 0.2 mm. 
     
     
       5. The coupling of claim 1, further including an entrance enlargement (13) formed in the entrance plug element at the side remote from the exit or coupling plug element, to enlarge the inlet of the duct (9) of the facilitating threading of the optical fiber element (2). 
     
     
       6. The coupling of claim 5, wherein said enlargement is essentially funnel-shaped and has an axial length of in the order of up to about 0.75 mm. 
     
     
       7. The coupling of claim 5, wherein the enlargement is funnel-shaped with a funnel angle (12) of about 60°. 
     
     
       8. The coupling of claim 1, wherein the channels or ducts (9) are enlarged at the edge portions of the plug elements facing another plug element to facilitate threading of the optical fiber element through said channel or duct (9). 
     
     
       9. The coupling of claim 1, further including at least one intermediate plug element (6,6a) located between the entrance plug element and the exit or coupling plug element (5), said intermediate plug element being formed with facing end surfaces which are in engagement with matching end surfaces of another and adjacent plug element, throughout essentially the entire area thereof. 
     
     
       10. The coupling of claim 9, wherein the channel or duct (9), at least at the side facing the entrance plug element (7) is slightly enlarged at the edge portion of the flat surface facing said entrance plug element. 
     
     
       11. The coupling of claim 1, wherein the plug elements comprise synthetic rubies or sapphires. 
     
     
       12. The coupling of claim 1, wherein the sleeve (4) comprises a hard metal sleeve. 
     
     
       13. Optical fiber structure comprising two optical fiber couplings   as claimed in claim 1   and a holding connection (20) connecting said fiber couplings together, with said polished surfaces (15,15') of the exit or coupling plug elements (5,5'), and the respective optical fiber elements (2,2') in engagement with each other, said predetermined projecting distance of each of said exit or coupling plug elements defining a gap between the respective holding sleeves (4,4') of said fiber couplings (1,1').   
     
     
       14. The coupling of claim 13, wherein said predetermined projecting distance (17) of the polished surface (15) beyond the terminal end of the sleeve (16) is between about 0.005 mm and 0.5 mm. 
     
     
       15. The coupling of claim 14, wherein said projecting distance is between about 0.01 mm and 0.2 mm. 
     
     
       16. The coupling of claim 13, further including an entrance enlargement (13) formed in the entrance plug element at the side remote from the exit or coupling plug element, to enlarge the inlet of the duct 9 and for facilitating threading of the optical fiber element (2). 
     
     
       17. The coupling of claim 13, further including at least one intermediate plug element (6,6a) located between the entrance plug element and the exit or coupling plug element (5), said intermediate plug element being formed with facing end surfaces which are in engagement with matching end surfaces of another and adjacent plug element, throughout essentially the entire area thereof. 
     
     
       18. The coupling of claim 17, wherein the channel or duct (9,9') of at least one of said plug elements (5,6,6a,7; 5',6',6a',7') at an edge portion facing an adjacent plug element is enlarged with respect to the remainder of the channel or duct. 
     
     
       19. The coupling of claim 13, wherein the plug elements comprise synthetic rubies or sapphires.